Attic ladders are used for the purpose of granting access to areas above or below a room or floor in which limited space is available. One key feature of the attic ladder is its ability to fold or retract upward into the ceiling in order to take up no floor space except when extended. Other advantages to the use of foldable attic ladders are the low cost and ease of manufacturing relative to typical fixed stairways. A key part of a foldable ladder is a strut. A strut is used to counteract the weight of a foldable ladder. Some foldable ladders are installed in an opening in a ceiling and are stowable above the ceiling. Typically, the stowed ladder is pulled down from the ceiling.
Examples of attic ladders or “disappearing stairways” are shown, for example, in U.S. Pat. Nos. 2,649,237 and 2,852,176. These ladders normally fold and retract upwardly into a frame secured between adjacent joists of the attic, and the folded ladder is covered by a door which normally extends substantially flush with the finished ceiling of the room in which the ladder is mounted.
The use of struts, such as a gas strut, in an attic ladder assembly permits single person installation of the attic ladder. In previous designs, one end of the strut is attached to the attic ladder while the other end is attached to a moveable lever arm attached to the upper section of the attic ladder. Attic ladders according to the present disclosure simplify ladder installation and reduce the cost and complexity of ladder for the manufacturer.
U.S. Pat. No. 4,281,743 shows another conventional attic ladder. As shown in FIGS. 1A and 1B, attic ladder 111 includes an outside frame 112 mounted between adjacent floor joists 113 of the attic floor 114. Cross braces 115 are mounted between a pair of adjacent floor joists 113 to provide end support for the frame 112 of the ladder. Ladder 111 is mounted in the ceiling by securing frame 112 to the joists 113 and the cross braces 115. A cover panel 116 forms part of ladder 111 and is hinged to the outer frame 112, so that the door becomes substantially flush with the ceiling 119 when the ladder 111 is folded. A first ladder portion 117 is affixed to the inner face of cover panel 116 and a second ladder portion 118 is pivotally hinged to the first ladder portion so as to be unfolded or folded when the ladder is opened or closed. While commercially available attic ladders or disappearing stairways typically come in a number of sizes, most come in several standard widths and lengths adaptable to fit conventional constructions.
U.S. Pat. No. 4,541,508 shows yet another conventional attic ladder. In FIG. 2, a foldable ladder is shown to consist of a lower section 211, a central section 212 and an upper section 213. The central section 212 is hingedly connected to the two remaining sections 211, 213 by a hinge so that the central section 212 and the lower section 211 can be folded up on the upper section 213. Upper section 213 is hingedly attached to a frame 214 by hinges 215, with the folding down movement of the upper ladder section 213 being limited by a pair of toggle joints 216 attached to the upper ladder section and to the frame 214. Toggle joints 216 are rigidly connected to each other at the lower arms by means of an axle 218 extending in parallel with the rungs of the ladder and are attached to the axle outside the side rails of the ladder. The ladder is spring-biased to a closed position by a gas spring 219 connected at one end to an outside of one side rail and connected at its other end, via piston rod 219a, to moment arm 218a, which is rigidly connected to the axle 218 at such an angle that a maximum moment is generated when the door is almost entirely closed. When the point of connection between the gas spring 219 and the moment arm 218a has passed the line for moment center (i.e. the connecting line between the attachment of the gas spring 219 to the ladder 213 and the axle 218, which passing takes place when the door is opened entirely), the gas spring 219 actuates the door so that it is locked in folded-down position, which is necessary because the “weight” of the door decreases as soon as the ladder sections are folded out.